1. Field of the Invention
The present invention pertains to a device for incorporating the leading edge of chain stitches, threads or strings from sewing machines and the like, into the initial stitches of the workpiece to prevent the unravelling of the stitches or strings while producing a stitch that is even with and locked into the leading edge of the workpiece. More particularly the invention relates to a semi-automatic device which is economical to operate, does not interfere with standard sewing techniques and which incorporates the leading edge of stitches in the initial stitches in the underside of the workpiece.
The incorporation of the leading edge of chain stitches or thread in the underside of the workpiece is achieved by the utilization of a novel clamping and cutting apparatus which when engaged operates automatically to clamp and sever the stitches between successive workpieces while maintaining the alignment of the thread so that it can be incorporated in the seam in the reverse side of the garment in the initial stitches of the workpiece. The novel apparatus employs a pneumatically activated clamp and knife combination which upon activation first closes to engage and maintain the thread in alignment and thereafter results in the activation of a pivotable knife which coacts with the clamp to provide a scissor-like action to separate the trailing edge of stitches from the leading edge of stitches that are thereafter released at a predetermined point in the stitching cycle for incorporation in the leading edge of the workpiece.
2. Description of the Prior Art
The prior art includes a variety of devices for cutting chain stitches and for incorporating chains of stitches in workpieces. A number of the prior art devices pertain only to cutting or severing chain stitches while other devices pertain to a combination of cutting and including the leading edge of the chain stitch in a workpiece or garment. The effectiveness of a particular combination for incorporation of stitches into a workpiece or garment depends not only upon its reliability but also on such factors as the quality of the finished product, complexity of the mechanical device involved and the cost of installation and operation of the device. Furthermore, additional factors such as the compatability of the device with the normal sewing operation of the sewing or stitching machine operator are important in determining productivity and hence the subsequent acceptance of such latchback or tieback devices.
The prior art pertaining to systems for cutting and severing chain stitches employs a variety of mechanical thread severing and stitch cutting devices which have been known in the industry as latchback, backtack, and tieback devices and have been available for use in chain stitching and over-edge sewing machines. These devices are generally utilized with over-edge sewing machines such as Federal stitch type 504 to incorporate the leading edge of a chain stitch into the sewn stitches of the workpiece to prevent the unravelling of the leading edge of the chain stitch. These latchback devices generally come as attachments but in most cases are built into sewing machines that are used for sewing shirts and garments and more particularly sleeve ends, cuff ends, binding ends and hemmed bottom ends and other types of operation where a Federal stitch type 504 is utilized and where it is desirable to lock the leading end of the stitch chain into the sewn article to thereby prevent its unravelling.
A number of the prior art latchback or tieback devices rely upon a vacuum to assist in the orientation of stitches after the separation of the stitches between workpieces. Representative of such prior art devices are Palacino U.S. Pat. No. 4,220,105; Marforio U.S. Pat. No. 4,038,933; Boucraut U.S. Pat. No. 3,490,403 and Launer U.S. Pat. No. 3,698,336. In Palacino '105, severed stitches are drawn by a vacuum to a gripping apparatus which maintains the stitches in a predetermined position with respect to the sewing needle so that the leading end of the stitches can be incorporated into the underside of the workpiece during the initial sewing operation on the next proceeding workpiece.
Unlike the present invention, Palacino orients stitches utilizing a guide and gripper means after the stitches have been severed. In addition, the gripper of Palacino is not released at a predetermined point in the sewing cycle but instead grips the stitches until the chain is pulled by the sewing machine from the gripping device. Other vacuum assisted prior art such as Marforio '933; Boucraut '403 and Launer '336 do not positively grip the chain of stitches but instead rely entirely upon the vacuum source to maintain the position of the chain as the sewing operation is initiated. As a result, the prior art fails to provide for the necessary adjustment of gripping force necessary for reliability and reproducibility of results for a variety of garments and stitching threads to prevent puckering which results when the stitches are held too long or a faulty lock for the stitches when they have not been tensioned sufficiently.
The prior art pertaining to the engaging and alignment of severed chain stitches as is represented by prior art such as Palacino U.S. Pat. No. 4,220,105; Marforio U.S. Pat. No. 4,038,933; Boucraut U.S. Pat. No. 3,490,403 and Launer U.S. Pat. No. 3,698,336 furthermore require extensive modification of sewing machines and in some cases are not compatible with existing equipment or the standard sewing techniques of sewing machine operators. In addition, such prior art devices are fairly expensive to install and to operate since a vacuum source is required to assist in the engagement and orientation of severed chain stitches.
Other prior art patents such as Lawber U.S. Pat. No. 2,756,704 and Palumbo U.S. Pat. No. 2,854,937 are representative of entirely manual and mechanical type devices for orienting, fixing and severing chain stitches from a preceeding garment which assist in the incorportion of the leading end of stitches into the subsequent garment. As will be recognized by those skilled in the art, prior art such as Lawber, '704 and Palumbo '937 do not provide for the incorporation of the chain stitch in the underside of the garment but instead incorporate the stitches on the topside or facing side of the garment. Such chain stitch devices consequently leave a detectable leading edge of the stitch on the top side of the garment which in many cases detracts from the saleability of an article. Typical devices such as these are discussed and critically evaluated in Palacino U.S. Pat. No. 4,220,105.
In addition to failing to incorporate the initial stitches in the preferred underside of the garment, such prior art devices do not provide a positive system for releasing the stitch chain at a predetermined point in the sewing cycle so that once the leading edge has been incorporated in the stitched garment for a predetermined distance the stitch chain is released to thereby prevent puckering of the garment that can otherwise result from a lengthy engagement of the strings during the sewing operation. As a result, many of the prior art devices available for incorporation of stitches in the leading edge of the garment have resulted in the stitches being too firmly tensioned into the initial stitches resulting in puckering or a too loose alignment of the initial stitches which results in misalignment and conceivable loss of proper stitch locking within the garment, which problem is compounded by variations in the speed of starting and running the stitching machine. In addition, many of the prior art latchback, tieback, and backtack devices unduly impede the traditional sewing techniques of the sewing machine operator and as such suffer the disadvantages of longer training periods and reduced productivity. Some of the prior art devices as a consequence of design, size, and disposition require extensive modification and have proved to be unduly expensive in their application to industrial stitching and sewing machine equipment.
The configuration and disposition of the novel latchback mechanism of the present invention is relatively compact and is disposed away from the congested area of stitching machine needle presser foot and throat plate combination and cooperates in conjunction therewith in a manner that does not impede the normal routine of the stitching machine operator in the stitching and removal of garments from traditional chain stitching machines. In addition, the semi-automatic device of the present invention provides greater reliability, increased productivity, and increased repeatability of incorporation of chain stitches in the leading edge of the garment since it does not impede the normal operation of the sewing machine operator nor result in the pulling of stitches from a clamping device resulting in puckering or result in too loose stitches being missed in the stitch locking operation.